GRAM-NEGATIVE FACULTATIVELY-ANAEROBIC RODS CHARACTERISTICS OF ENTEROBACTERIACEAE · Gram-negative, straight rods · Can be motile (peritrichous) or non-motile · Non-sporulating · Facultative anaerobes · Production of acid from glucose · Catalase +ive · Oxidase -ive GENERAL MICROBIOLOGY SALMONELLA · Nomenclature = typhoidal (typhoid fever) / non-typhoidal (food poisoning) . Peritrichous - motile · Diameter = 0.7 - 1.5 um · Length = 2-5 um · Growth conditions: · Temperature 5.5 - 45.6°? · pH 3.8 - 9.5 · Aw 0.99 GENERAL MICROBIOLOGY E. COLI · Peritrichous - motile · Growth conditions: · Temperature 10 - 55°C · pH 4.5 - 9 · Aw 0.96 - 7% NaCl · Habitat = commensal (human + warm blooded animals) Main Groups of Pathogenic E.coli: · Enteropathogenic (EPEC) = infant diarrhoea · Entertoxigenic (ETEC) = travellers diarrhoea · Enteroinvasive (EIEC) = fresh blood-dysentery breaks through wall of gut · Enterohemoryhagic (EHEC) = blood in faeces · First isolated in 1974 in Canada · Main serogroups = 0157 and 026 (type of antigen on cell surface) . O157 = acid and desiccation resistant - important virulence factor · Verocytotoxin (VTEC/STEC) RELATING INCIDENCE AND EPIDEMIOLOGY OF SALMONELLA · 1940s = lowest number of cases (WW2) . 1953 - 1954 = rapid increase in meat and egg consumption . 1959 = surge in infections linked to hen's eggs · 1980s = enteritidis phage type 4 (PT4) identified as most prevalent serotype and the leading cause of food borne infection linked to shelled eggs · Result = all eggs in UK and USA pasteurised and washed to effectively remove faecal contamination · 1990s = Edwina Curry's statement - sales of eggs plummeted . 2002 = introduction of Nobilis Salenvac administered to laying chickens · Stimulates the production of maternally derived antibodies against S. Enteritidis in chick before it hatches · All eggs vaccinated had a red lion stamp SYMPTOMS OF SALMONELLA AND STEC-0157 INFECTIONS Symptoms of Salmonella · 12 - 72hrs = nausea, vomiting, fever, diarrhoea, abdominal cramps · 4 - 7 days = illness ranges mild to severe (most recover without treatment)
Symptoms of E.coli · EHEC · Incubation 3-9 days . Duration 2-9 days · ID = < 100 organisms PATHOGENIC MECHANISMS Salmonella Mechanism of Infection 1. Salmonella enters body by consumption of contaminated food 2. Stomach acid can reduce and sometimes eliminate the salmonella but some can get through to the intestine, attaching then penetrating cells 3. Toxins produced by the bacteria (enterotoxin and cytotoxin) can damage and kill the cells that line the intestines which results in intestinal fluid loss (diarrhoea) 4. Some salmonella can survive in the immune system and can reach the bloodstream causing a systemic infection - Type 3 secretion system = provides virulence factors to host cell and interferes with host cell signalling - SPI1 and SPI2 - Like a molecular injection = pokes toxins into cells - Causes the death of intestinal cells (fluid loss and diarrhoea) E. Coli Mechanism of Infection · Intimate binding = Intimin / Tir of